The present proposal is focused on two major issues: understanding what cognitive mechanisms account for age differences in memory function in older adults and exploring how these mechanisms relate to the ability of older adults to use supportive contextual information to enhance their memory function. We postulate that age-differences in memory function and older adults' ability to use context can be accounted for in terms of a single construct: the construct of mental effort. In the past, this has been viewed as an untestable idea by many memory theorists, as it has proven impossible to independently measure the amount of cognitive resources that a subject brought into a situation and relate this resource to the demands created by the memory task. We believe that recent work in our laboratory and in a few other labs (Salthouse; Lindenberger, Mayr, & Kliegl; Hultsch, Hertzog, & Dixon) have developed good ways to get estimates of cognitive resources. In this research, we propose to use a combination of individual differences methodologies and more traditional experimental procedures to understand the role of mental effort in accounting for patterns of age differences across many types of memory and to explain the effects of memory context on remembering. Specifically, we propose to determine the roles of processing resource (operationalized as the joint effects of perceptual speed and working memory) and existing knowledge structures to explain age differences and cases of age invariance in use of context across different types of memory. We propose to restructure the environmental support view of context and aging within a more precisely specified continuum of mental effort. In Experiments 1 and 2, we use structural equation models to examine how constructs measuring cognitive resource and world knowledge contribute to age differences across many types of memory. In Experiment 3 and 4, we examine how context which is highly effortful to use, may not only fail to support memory in older adults, but may actually be more problematic for them then receiving no contextual support at all. In Experiment 5, we examine age differences in the deliberate recollection and familiarity components of memory. We determine how these components differ in their contribution to memory depending on whether the associative context of the memory task is easy or hard to use for older adults. In Experiments 6 and 7, we look at how effort and task demands affect prospective memory, and in Experiment 8, we examine the role of environmental context as a type of memory support for older adults.